This project continues the study of fibroblast cultures from children with leukemia, their first, second, and third degree relatives, individuals with other genetic disorders, and individuals with and without oncogenic disorders. Two principal markers have been studied, the ability of SV40 virus to transform the cell cultures and the production of early and late T-antigen and its duration. The number of transformed foci in the tissue cultures will continue to be studied and scored in the same manner as previously. 236 fibroblast cultures from such individuals have now been collected, grown (to the fifth passage), and stored in liquid nitrogen. Over 88 such cultures have been studied by such markers and it is proposed that the marker studies will continue until all stored cultures have been completed. Thus, we will attempt to determine whether there is a correlation between the degree of cell transformation in such cultured cells, cytogenetic instability, and the incidence of leukemia in the children involved. Since a large number of fibroblast cultures have been developed and approximately one-fourth of these with regard to the markers have been studied, we feel that the continuance of this project to its completion will be a significant aspect of the investigation of childhood leukemia.